How can I catch AWT thread exceptions in Java?

Question

We'd like a trace in our application logs of these exceptions - by default Java just outputs them to the console.

Answer 1

There is a distinction between uncaught exceptions in the EDT and outside the EDT.

Another question has a solution for both but if you want just the EDT portion chewed up...

class AWTExceptionHandler {

  public void handle(Throwable t) {
    try {
      // insert your exception handling code here
      // or do nothing to make it go away
    } catch (Throwable t) {
      // don't let the exception get thrown out, will cause infinite looping!
    }
  }

  public static void registerExceptionHandler() {
    System.setProperty('sun.awt.exception.handler', AWTExceptionHandler.class.getName())
  }
}

Answer 2

Since Java 7, you have to do it differently as the sun.awt.exception.handler hack does not work anymore.

Here is the solution (from Uncaught AWT Exceptions in Java 7).

// Regular Exception
Thread.setDefaultUncaughtExceptionHandler(new ExceptionHandler());

// EDT Exception
SwingUtilities.invokeAndWait(new Runnable()
{
    public void run()
    {
        // We are in the event dispatching thread
        Thread.currentThread().setUncaughtExceptionHandler(new ExceptionHandler());
    }
});

Answer 3

A little addition to shemnons anwer:
The first time an uncaught RuntimeException (or Error) occurs in the EDT it is looking for the property "sun.awt.exception.handler" and tries to load the class associated with the property. EDT needs the Handler class to have a default constructor, otherwise the EDT will not use it.
If you need to bring a bit more dynamics into the handling story you are forced to do this with static operations, because the class is instantiated by the EDT and therefore has no chance to access other resources other than static. Here is the exception handler code from our Swing framework we are using. It was written for Java 1.4 and it worked quite fine there:

public class AwtExceptionHandler {

    private static final Logger LOGGER = LoggerFactory.getLogger(AwtExceptionHandler.class);

    private static List exceptionHandlerList = new LinkedList();

    /**
     * WARNING: Don't change the signature of this method!
     */
    public void handle(Throwable throwable) {
        if (exceptionHandlerList.isEmpty()) {
            LOGGER.error("Uncatched Throwable detected", throwable);
        } else {
            delegate(new ExceptionEvent(throwable));
        }
    }

    private void delegate(ExceptionEvent event) {
        for (Iterator handlerIterator = exceptionHandlerList.iterator(); handlerIterator.hasNext();) {
            IExceptionHandler handler = (IExceptionHandler) handlerIterator.next();

            try {
                handler.handleException(event);
                if (event.isConsumed()) {
                    break;
                }
            } catch (Throwable e) {
                LOGGER.error("Error while running exception handler: " + handler, e);
            }
        }
    }

    public static void addErrorHandler(IExceptionHandler exceptionHandler) {
        exceptionHandlerList.add(exceptionHandler);
    }

    public static void removeErrorHandler(IExceptionHandler exceptionHandler) {
        exceptionHandlerList.remove(exceptionHandler);
    }

}

Hope it helps.

Answer 4

There are two ways:

1. /* Install a Thread.UncaughtExceptionHandler on the EDT */
2. Set a system property: System.setProperty("sun.awt.exception.handler",MyExceptionHandler.class.getName());

I don't know if the latter works on non-SUN jvms.

--

Indeed, the first is not correct, it's only a mechanism for detecting a crashed thread.